1. Field of Invention
This invention pertains to a variable volume drain field system for onsite wastewater renovation. More particularly, this invention pertains to a variable volume drain field system that displaces wastewater, stores wastewater, and has differential release of the stored wastewater.
2. Description of the Related Art
Conventional drain field systems include a trench dug into the ground. The trench contains a wastewater delivery pipe that is surrounded with aggregate. The trench is covered with earth. The wastewater delivery pipe is typically a corrugated flexible pipe with perforations that allow the wastewater to exit the pipe. The aggregate is typically rock, crushed stone, chipped tires, and/or other materials that maintain voids and allow fluid to flow or percolate through the aggregate. The aggregate prevents the sidewalls of the trench from collapsing and prevents soil intrusion into the perforations of the pipe. Such prior art drain field systems are describe in U.S. Pat. Nos. 5,015,123 and 5,549,415. One prior art variation on the standard perforated corrugated pipe for the wastewater delivery pipe is described in U.S. Pat. No. 4,134,268.
In conventional drain fields, wastewater enters the trench through the pipe, and the wastewater collects first on the trench floor where it percolates or is absorbed into the soil. If the volume of wastewater flowing into the trench is greater than the uptake capacity of the trench bottom, the wastewater begins to fill the trench. As the wastewater rises, the wastewater is absorbed by the portion of the sidewalls of the trench that are submerged. Accordingly, the trench bottom typically receives the most wastewater with the sidewalls receiving little use, until, over a period of time, the absorptive capacity of the trench bottom decreases due to anaerobic decomposition or bioslime accumulation.
Innovations have been made with respect to the conventional drain field design. U.S. Pat. No. 5,015,123 issued to Houck, et al., on May 14, 1991, and U.S. Pat. No. 5,051,028 issued to Houck, et al., on Sep. 24, 1991, both titled “Method and apparatus for installation of drainage field,” disclose a corrugated perforated conduit 10 encased in a nylon netting or mesh, which is filled with an aggregation of discrete, water impervious, crush resistant lightweight elements to form a preassembled drainage line unit 20. A conduitless casing unit 30 is constructed in a similar manner, but without the conduit 10. A pair of conduitless casings 30 are placed in the bottom of trench 12 with the preassembled drainage line unit 20 placed on top of the pair of casings 30 and the trench 12 is filed with topsoil 16.
U.S. Pat. No. 5,516,229 issued to Atchley, et al., on May 14, 1996, and U.S. Pat. No. 5,520,481 issued to Atchley, et al., on May 28, 1996, both titled “Drain field system,” disclose a drain field assembly 10 of a bundle of perforated pipes 20, 30 covered on top 104 and the sides 106, 108 with a protective sheeting 102. The assembly includes one or more distribution pipes 20 that deliver wastewater to the trench and the remainder are void pipes 30 that replace the aggregate normally used in trenches.
U.S. Pat. No. 6,443,652, issued to Houck, et al., on Sep. 3, 2002, titled “Aggregate chamber leach lines for leaching effluent and associated method,” discloses a chamber type drainage system that includes chamber portions 38 created under a cap 32 on either side of a support member 32. The chambers 38 allow the temporary storage of excess volumes of effluent, so that the drain field does not backup by suddenly filling with wastewater when demand on the system is greatest. The chamber 38 is bounded on two sides by aggregate drainage lines 36 that include a perforated pipe encased in a mesh that is filled with a lightweight aggregate, such as disclosed in U.S. Pat. No. 5,015,123, discussed above.
Another innovation in conventional drain field design is disclosed in U.S. Pat. No. 4,759,661, issued to Nichols, et al., on Jul. 26, 1988, titled “Leaching system conduit.” U.S. Pat. No. 5,511,903, issued to Nichols, et al., on Apr. 30, 1996, titled “Leaching chamber with perforated web sidewall,” followed the first Nichols patent. The Nichols' leaching chamber disclosed in the first patent is a device 20 in the shape of an inverted trough, that is, it is arch-shaped in cross-section. The device 20 is buried under earth without any aggregate. Effluent 50 is delivered to the device 20 by a pipe 44 and the effluent is primarily absorbed into the soil 52 at the open bottom of the device 20 and then at the sides of the device 20 when the effluent inflow is greater than the uptake at the bottom.
Several of the above-described innovations provide for displacing the aggregate to allow greater storage capacity of the wastewater. For example, U.S. Pat. No. 5,516,229 discloses perforated pipes 30 positioned adjacent distribution pipes 20, U.S. Pat. No. 6,443,652 discloses chambers 38 free of aggregate, and U.S. Pat. No. 4,759,661 discloses a device 20 that replaces the aggregate.
However, in addition to increased storage capacity, it is also advantageous to utilize the walls of the trench and not just the bottom surface for wastewater absorption. Additionally, it is advantageous to release the stored wastewater in such a manner to maximize the surface area of the trench used to absorb the wastewater.